1. Technical Field of the Invention
This invention relates to a polyolefin film and, in particular, to a multiple-layer polyolefin film.
2. Background of the Art
Polyolefin films are widely employed as packaging wrappers for articles of commerce, and are eminently suitable for this purpose. However, for certain packaging applications in which, for example, the wrapped article may be subjected to impact or exposed to contact with relatively sharp or abrasive objects while in transit or during handling, it is desirable to provide a film wrapper exhibiting improved impact strength and puncture resistance. An apparent solution to the problem would be to increase the thickness of the film. However, the nature of the polymeric film-forming process is such that when a sufficiently thick cast extrudate is formed, the resultant film exhibits inherent profile defects and inferior optical characteristics. It has therefore been proposed to provide a thick polymeric film by forming a laminate of two, more, plies of relatively thin film. For example, U.S. Pat. No. 3,554,833 exemplifies a blown film technique wherein an extruded, single wall tubular film of molten polyethylene is inflated and subsequently flattened, while the interior surfaces of the tube are in a semi-molten condition, by passing the tube between a pair of rotating, pressure nip rolls, and then cooling the resultant laminate to a permanent set condition.
Attempts to prepare laminates of polymers or higher alpha monoolefins, containing 3 or more carbon atoms in the molecule, by collapsing a tubular film, have not been particularly successful. Defects encountered include poor interlaminar adhesion, entrapment of gas bubbles between the layers of the laminate, and poor optical characteristics.
We have now devised an improved multiple-layer polyolefin film.